Amines vanadium!!! complexes

The co-ordination chemistry of vanadium(n) has been extended by the preparation and characterization of complexes with aliphatic and heterocyclic amines.365 Intense charge-transfer bands dominate the reflectance spectrum of the dark-red or red-brown V(amine)4X2 complexes (amine = py, / - and y-picoline X = Cl, Br, or I) but assignments of some of the d-d transitions indicate a trans-dihalogeno structure this is consistent with the spin-only magnetic moments ca. 3.87 BM. In contrast, the yellow V(amine)2Br2 complexes obtained with / - and y-picoline exhibit considerable antiferromagnetic interaction indicative of polymeric bromine-bridged structures. 

However if one looks at table 1 in more detail, it is difficult to understand why the vanadium complex of the N-hydroxy compound should be more stable than the vanadium compound of IDP on the basis of the structure proposed with a bond to nitrogen. Normaly one would assume that the nitrogen in a hydroxylamine derivative is less basic as in an amine, and therefore also the complex stability decreases. Table 1 teaches this for calcium, nickel, copper and zinc complexes of both ligands. With the exception of vanadium all other metal complexes of IDP are approximately by one order of magnitude more stable than those one of HIDP. 

Sheng and Zajacek [182] have shown that vanadium complexes are somewhat superior catalysts to molybdenum. Both give good selectivity to amine oxide but reaction rates are faster when vanadium complexes are used. Compounds of tungsten, niobium and tantalum were poorer catalysts whereas chromium, cobalt, manganese and iron complexes were ineffective. 

Reul BA, Amin SS, Buchet JP, Ongemba LN, Crans DC, Brichard SM. 1999. Effects of vanadium complexes with organic ligands on glucose metabolism a comparison study in diabetic rats. BrJ Pharmacol 126 467-477. 

Hu and coworker developed the silica, titania, ceria, and y-alumina supported vanadium catalyst, which shown unique reactivity for the direct amination of toluene with hydroxylamine hydrochloride, over 50 % total yield of toluidines was obtained on the y-alumina supported vanadium catalyst operated at optimal conditions [87]. They also investigated a sodium metavanadate catalyzed one-step amination of benzene to aniline with hydroxylamine [88], The reaction became more efficient in the presence of oxygen. A free-radical mechanism was proposed based on the results of EPR, NMR, and UV-Vis characterization. Moreover, the catalytic activity of a series of vanadium complexes with N,0- or 0,0-ligands for the liquid-phase direct amination of benzene with hydroxylamine to aniline has been investigated [89]. [VO(OAc>2] was proved to be the most active catalyst for the amination because of its relatively greater electrophilicity and smaller steric hindrance of ligand. 

Lu YF, Zhu LF, Liu QY, Guo B, Hu XK, Hu CW (2009) Direct amination of benzene to aniline with several typical vanadium complexes. Chin Chem Lett 20 238-240... 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

The ion-pair complex formed by the interaction of hydroxobis(8-quinolyloxo) vanadium (V) [VOQ2OH] and /i-butyl amine is also effective in photoinitiation of polymerization of MMA in bulk and in solution [40]. The quantum yield of initiation and polymerization determined are equal to 0.166 and 35.0, respectively. Hydroxyl radical ( OH) is reported to be the initiating radical and the following photoreaction is suggested ... 

It is quite often possible to prepare hydroxypyridinone complexes directly by one-pot synthesis from the appropriate hydroxypyranone, amine, and metal salt 90-92). They can also be prepared by reacting complexes such as P-diketonates with hydroxypyridinones (see e.g., Ce, Mo later). Several maltolate complexes, of stoichiometry ML2, ML3, ML4, or MOL2, have been prepared by electrochemical oxidation of the appropriate metal anode, M — a first-row d-block metal (Ti, V, Cr, Mn, Fe, Co, Ni), In, Zr, or Hf, in a solution of maltol in organic solvent mixtures 92). Preparations of, e.g., manganese(III), vanadium(III), or vanadium(V) complexes generally involve oxidation... 

The most active d metal peroxo complexes toward nucleophilic substrates, like amines, phosphines, thioethers, double bonds etc., are molybdenum, tungsten and rhenium derivatives vanadium and titanium catalysis is also important, in particular when... 

Complexes [VL3]X2 (L = en, 1,2-diaminopropane, 1,3-diaminopropane X = C1, Br, I) and [V(dien)2]X2 were prepared by mixing ethanolic solutions of amine and of vanadium(II) halide. The magnetic moments (3.66-3.91 BM) and electronic spectra were typical of octahedral vanadium(II) and there was no halogen coordination.65... 

Somewhat surprisingly, maltol (2-methyl-3-hydroxy-4-pyrone), an aromatic analogue to a-hydroxy carboxylic acids, shows little inclination toward formation of dimeric complexes. Rather, the chemistry is more in parallel with that of oxalate, and an x-ray structure of the bismaltolato complex [25] shows a cis octahedral coordination similar to that found for the oxalate complex. Under mildly acidic to moderately basic solution, the major complexes are mono- and bisligand derivatives. The corresponding vanadium chemical shifts are -509 and -496 ppm, respectively [25,26], The closely related amines, 2-methyl-3-hydroxy-4-pyridinone and its N-... 

Like other amines, pyridines and anilines readily form hetero complexes, and this has provided a means of studying the influence of substituent electronegativity on vanadium chemical shifts. Hammett plots for a number of anilines and pyridines revealed a linear relationship between substituent electronegativity and chemical shifts and showed, for both classes of ligands, that51V chemical shifts became more... 

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